1. Field of the Invention
The present invention relates to piezoelectric shear resonators and composite piezoelectric shear resonators. More specifically, the present invention relates to a piezoelectric shear resonator for use, for example, as a vibrating member in a composite piezoelectric shear resonator and also relates to a composite piezoelectric shear resonator, except an energy-trap resonator, using the piezoelectric shear resonator as a vibrating member.
The present invention further relates to composite piezoelectric shear resonators and piezoelectric resonator components. More particularly, the present invention relates to a composite piezoelectric shear resonator having a configuration in which vibrations propagating to a reflective layer from a vibrating member are reflected at an interface between the reflective layer and a holding member and also relates to a piezoelectric resonator component including the composite piezoelectric shear resonator.
2. Description of the Related Art
Piezoelectric resonators for use as a piezoelectric oscillator or a bandpass filter (BPF) are disclosed in, for example, Japanese Unexamined Patent Application Publications Nos. H5-243889 and H7-147527. A thickness-shear piezoelectric vibrating element disclosed in the publication No. H5-243889 has a configuration in which excitation electrodes are provided on two opposing major surfaces of a LiTaO3 piezoelectric substrate. This piezoelectric vibrating element is characterized in that the relationship between the overlapping length of the opposing excitation electrodes and the thickness of the piezoelectric substrate is adjusted within an appropriate range to inhibit an unwanted ripple that is generated in the vicinity of the resonant frequency.
Meanwhile, a piezoelectric resonator disclosed in the publication No. H7-147527 has a configuration in which resonance electrodes are arranged to oppose each other on two longer side major surfaces of a piezoelectric element having rectangular surfaces, and is characterized in that the ratio of the length of the longer-side edge to the length of the shorter-side edge is adjusted in relation to Poisson's ratio. With such a piezoelectric resonator, adopting a certain length ratio allows for an improvement in the energy-trapping efficiency of a resonating portion, thus providing an advantage in that miniaturization of the piezoelectric resonator can be achieved.
Meanwhile, what is disclosed in the publication No. H5-243889 is a so-called typical “energy-trapping piezoelectric shear resonator”. Such a configuration, however, makes it difficult to provide a thickness-shear resonator having a large specific band (i.e., the ratio of the passband width to the center frequency). Energy trapping typically refers to a vibration phenomenon in which vibration energy is concentrated in the vicinity of the overlapping portion of excitation electrodes. The piezoelectric shear resonator having the above-described configuration is not suitable for miniaturization since it involves a large amount of area for providing a vibration damping region, i.e., a region between a vibrating portion to a non-vibrating portion.
In contrast, while the piezoelectric shear resonator disclosed in the publication No. H7-147527 is also an energy-trapping resonator, it allows for further miniaturization compared to a typical energy-trapping resonator since the energy-trapping efficiency is substantially improved. In practice, however, even such a piezoelectric shear resonator cannot provide an increased specific band.